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From: wenyang.linux@foxmail.com
To: "Eric W . Biederman" <ebiederm@xmission.com>,
	Luis Chamberlain <mcgrof@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Joel Granados <j.granados@samsung.com>,
	Christian Brauner <brauner@kernel.org>
Cc: Wen Yang <wenyang.linux@foxmail.com>,
	Iurii Zaikin <yzaikin@google.com>,
	linux-kernel@vger.kernel.org
Subject: [PATCH v2 1/9] sysctl: support encoding values directly in the table entry
Date: Sat,  9 Mar 2024 18:31:18 +0800
In-Reply-To: <cover.1709978655.git.wenyang.linux@foxmail.com>
References: <cover.1709978655.git.wenyang.linux@foxmail.com>
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From: Wen Yang <wenyang.linux@foxmail.com>

Eric points out: "by turning .extra1 and .extra2 into longs instead of
keeping them as pointers and needing constants to be pointed at somewhere
.. The only people I can see who find a significant benefit by
consolidating all of the constants into one place are people who know how
to stomp kernel memory."

This patch supports encoding values directly in table entries through the
following work:
- extra1/extra2 and min/max are placed in one union to ensure that the
  previous code is not broken, then we have time to remove unnecessary
  extra1/extra2 progressively;
- since type only has two states, use one bit to represent it;
- two bits were used to represent the information of the above union( 0:
  using extra1/extra2, 1: using min, 2: using max, 3: using both min/max);
- added some helper macros.

Suggested-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Wen Yang <wenyang.linux@foxmail.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Joel Granados <j.granados@samsung.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Iurii Zaikin <yzaikin@google.com>
Cc: linux-kernel@vger.kernel.org
---
 include/linux/sysctl.h | 108 ++++++++++++++++++++++++++++++++++++++---
 kernel/sysctl.c        |  61 +++++++++++++++++------
 2 files changed, 148 insertions(+), 21 deletions(-)

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index ee7d33b89e9e..1ba980219e40 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -61,6 +61,25 @@ extern const int sysctl_vals[];
 
 extern const unsigned long sysctl_long_vals[];
 
+#define	SYSCTL_NUMERIC_NEG_ONE			((long)-1)
+#define	SYSCTL_NUMERIC_ZERO			(0L)
+#define	SYSCTL_NUMERIC_ONE			(1L)
+#define	SYSCTL_NUMERIC_TWO			(2L)
+#define	SYSCTL_NUMERIC_THREE			(3L)
+#define	SYSCTL_NUMERIC_FOUR			(4L)
+#define	SYSCTL_NUMERIC_ONE_HUNDRED		(100L)
+#define	SYSCTL_NUMERIC_TWO_HUNDRED		(200L)
+#define	SYSCTL_NUMERIC_THREE_HUNDRED		(300L)
+#define	SYSCTL_NUMERIC_FIVE_HUNDRED		(500L)
+#define	SYSCTL_NUMERIC_ONE_THOUSAND		(1000L)
+#define	SYSCTL_NUMERIC_TWO_THOUSAND		(2000L)
+#define	SYSCTL_NUMERIC_THREE_THOUSAND		(3000L)
+#define	SYSCTL_NUMERIC_16K			(16384L)
+#define	SYSCTL_NUMERIC_U8_MAX			((long)U8_MAX)
+#define	SYSCTL_NUMERIC_U16_MAX			((long)U16_MAX)
+#define	SYSCTL_NUMERIC_INT_MAX			((long)INT_MAX)
+#define	SYSCTL_NUMERIC_LONG_MAX			(LONG_MAX)
+
 typedef int proc_handler(struct ctl_table *ctl, int write, void *buffer,
 		size_t *lenp, loff_t *ppos);
 
@@ -131,6 +150,18 @@ static inline void *proc_sys_poll_event(struct ctl_table_poll *poll)
 #define DEFINE_CTL_TABLE_POLL(name)					\
 	struct ctl_table_poll name = __CTL_TABLE_POLL_INITIALIZER(name)
 
+enum {
+	SYSCTL_TABLE_TYPE_DEFAULT,
+	SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY
+};
+
+enum {
+	SYSCTL_TABLE_EXTRA_PTR,
+	SYSCTL_TABLE_EXTRA_LONG_INIT_MIN,
+	SYSCTL_TABLE_EXTRA_LONG_INIT_MAX,
+	SYSCTL_TABLE_EXTRA_LONG_INIT_MINMAX
+};
+
 /* A sysctl table is an array of struct ctl_table: */
 struct ctl_table {
 	const char *procname;		/* Text ID for /proc/sys, or zero */
@@ -138,20 +169,39 @@ struct ctl_table {
 	int maxlen;
 	umode_t mode;
 	/**
-	 * enum type - Enumeration to differentiate between ctl target types
+	 * type - Indicates to differentiate between ctl target types
 	 * @SYSCTL_TABLE_TYPE_DEFAULT: ctl target with no special considerations
 	 * @SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY: Used to identify a permanently
 	 *                                       empty directory target to serve
 	 *                                       as mount point.
 	 */
-	enum {
-		SYSCTL_TABLE_TYPE_DEFAULT,
-		SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY
-	} type;
+	u8 type:1;
+
+	/**
+	 * extra_flags
+	 * @SYSCTL_TABLE_EXTRA_PTR: flag indicating that this uses extra1/extra2.
+	 * @SYSCTL_TABLE_EXTRA_LONG_INIT_MIN: flag indicating that this uses min/max
+					      and min has been initialized.
+	 * @SYSCTL_TABLE_EXTRA_LONG_INIT_MAX: flag indicating that this uses min/max
+					      and max has been initialized.
+	 * @SYSCTL_TABLE_EXTRA_LONG_INIT_MINMAX: flag indicating that this uses min/max
+						 and both have been initialized.
+	 *
+	 */
+	u8 extra_flags:2;
+	union {
+		struct {
+			void *extra1;
+			void *extra2;
+		};
+		struct {
+			long min;
+			long max;
+		};
+	};
+
 	proc_handler *proc_handler;	/* Callback for text formatting */
 	struct ctl_table_poll *poll;
-	void *extra1;
-	void *extra2;
 } __randomize_layout;
 
 struct ctl_node {
@@ -213,6 +263,50 @@ struct ctl_table_root {
 #define register_sysctl(path, table)	\
 	register_sysctl_sz(path, table, ARRAY_SIZE(table))
 
+#define CTL_TABLE_ENTRY(_name, _data, _len, _mode, _func)		      \
+	{								      \
+		.procname = _name,					      \
+		.data = _data,						      \
+		.maxlen = _len,						      \
+		.mode = _mode,						      \
+		.proc_handler = _func,					      \
+		.extra_flags = SYSCTL_TABLE_EXTRA_PTR,			      \
+	}
+
+#define CTL_TABLE_ENTRY_MIN(_name, _data, _len, _mode, _func, _min)	      \
+	{								      \
+		.procname = _name,					      \
+		.data = _data,						      \
+		.maxlen = _len,						      \
+		.mode = _mode,						      \
+		.proc_handler = _func,					      \
+		.min = _min,						      \
+		.extra_flags = SYSCTL_TABLE_EXTRA_LONG_INIT_MIN,	      \
+	}
+
+#define CTL_TABLE_ENTRY_MAX(_name, _data, _len, _mode, _func, _max)	      \
+	{								      \
+		.procname = _name,					      \
+		.data = _data,						      \
+		.maxlen = _len,						      \
+		.mode = _mode,						      \
+		.proc_handler = _func,					      \
+		.max = _max,						      \
+		.extra_flags = SYSCTL_TABLE_EXTRA_LONG_INIT_MAX,	      \
+	}
+
+#define CTL_TABLE_ENTRY_MINMAX(_name, _data, _len, _mode, _func, _min, _max)  \
+	{								      \
+		.procname = _name,					      \
+		.data = _data,						      \
+		.maxlen = _len,						      \
+		.mode = _mode,						      \
+		.proc_handler = _func,					      \
+		.min = _min,						      \
+		.max = _max,						      \
+		.extra_flags = SYSCTL_TABLE_EXTRA_LONG_INIT_MINMAX,	      \
+	}
+
 #ifdef CONFIG_SYSCTL
 
 void proc_sys_poll_notify(struct ctl_table_poll *poll);
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 157f7ce2942d..144c441236ab 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -822,6 +822,20 @@ struct do_proc_dointvec_minmax_conv_param {
 	int *max;
 };
 
+static void do_int_conv_param_init(const struct ctl_table *table,
+		struct do_proc_dointvec_minmax_conv_param *param)
+{
+	if (table->extra_flags == SYSCTL_TABLE_EXTRA_PTR) {
+		param->min = table->extra1;
+		param->max = table->extra2;
+	} else {
+		param->min = (table->extra_flags & SYSCTL_TABLE_EXTRA_LONG_INIT_MIN) ?
+			(int *)&table->min : NULL;
+		param->max = (table->extra_flags & SYSCTL_TABLE_EXTRA_LONG_INIT_MAX) ?
+			(int *)&table->max : NULL;
+	}
+}
+
 static int do_proc_dointvec_minmax_conv(bool *negp, unsigned long *lvalp,
 					int *valp,
 					int write, void *data)
@@ -867,10 +881,9 @@ static int do_proc_dointvec_minmax_conv(bool *negp, unsigned long *lvalp,
 int proc_dointvec_minmax(struct ctl_table *table, int write,
 		  void *buffer, size_t *lenp, loff_t *ppos)
 {
-	struct do_proc_dointvec_minmax_conv_param param = {
-		.min = (int *) table->extra1,
-		.max = (int *) table->extra2,
-	};
+	struct do_proc_dointvec_minmax_conv_param param;
+
+	do_int_conv_param_init(table, &param);
 	return do_proc_dointvec(table, write, buffer, lenp, ppos,
 				do_proc_dointvec_minmax_conv, &param);
 }
@@ -889,6 +902,20 @@ struct do_proc_douintvec_minmax_conv_param {
 	unsigned int *max;
 };
 
+static void do_uint_conv_param_init(const struct ctl_table *table,
+		struct do_proc_douintvec_minmax_conv_param *param)
+{
+	if (table->extra_flags == SYSCTL_TABLE_EXTRA_PTR) {
+		param->min = table->extra1;
+		param->max = table->extra2;
+	} else {
+		param->min = (table->extra_flags & SYSCTL_TABLE_EXTRA_LONG_INIT_MIN) ?
+			(unsigned int *)&table->min : NULL;
+		param->max = (table->extra_flags & SYSCTL_TABLE_EXTRA_LONG_INIT_MAX) ?
+			(unsigned int *)&table->max : NULL;
+	}
+}
+
 static int do_proc_douintvec_minmax_conv(unsigned long *lvalp,
 					 unsigned int *valp,
 					 int write, void *data)
@@ -936,10 +963,9 @@ static int do_proc_douintvec_minmax_conv(unsigned long *lvalp,
 int proc_douintvec_minmax(struct ctl_table *table, int write,
 			  void *buffer, size_t *lenp, loff_t *ppos)
 {
-	struct do_proc_douintvec_minmax_conv_param param = {
-		.min = (unsigned int *) table->extra1,
-		.max = (unsigned int *) table->extra2,
-	};
+	struct do_proc_douintvec_minmax_conv_param param;
+
+	do_uint_conv_param_init(table, &param);
 	return do_proc_douintvec(table, write, buffer, lenp, ppos,
 				 do_proc_douintvec_minmax_conv, &param);
 }
@@ -1038,8 +1064,16 @@ static int __do_proc_doulongvec_minmax(void *data, struct ctl_table *table,
 	}
 
 	i = data;
-	min = table->extra1;
-	max = table->extra2;
+	if (table->extra_flags == SYSCTL_TABLE_EXTRA_PTR) {
+		min = table->extra1;
+		max = table->extra2;
+	} else {
+		min = (table->extra_flags & SYSCTL_TABLE_EXTRA_LONG_INIT_MIN) ?
+			&table->min : NULL;
+		max = (table->extra_flags & SYSCTL_TABLE_EXTRA_LONG_INIT_MAX) ?
+			&table->max : NULL;
+	}
+
 	vleft = table->maxlen / sizeof(unsigned long);
 	left = *lenp;
 
@@ -1274,10 +1308,9 @@ int proc_dointvec_jiffies(struct ctl_table *table, int write,
 int proc_dointvec_ms_jiffies_minmax(struct ctl_table *table, int write,
 			  void *buffer, size_t *lenp, loff_t *ppos)
 {
-	struct do_proc_dointvec_minmax_conv_param param = {
-		.min = (int *) table->extra1,
-		.max = (int *) table->extra2,
-	};
+	struct do_proc_dointvec_minmax_conv_param param;
+
+	do_int_conv_param_init(table, &param);
 	return do_proc_dointvec(table, write, buffer, lenp, ppos,
 			do_proc_dointvec_ms_jiffies_minmax_conv, &param);
 }
-- 
2.25.1